A GPS (Global Positioning System) receiver is usually used in a moving vehicle (including ships) to figure out its location or in case the driver get lost. The GPS receiver is constructed in such a manner to receive satellite signals from the satellites orbiting the Globe in the predictable paths. The satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock, generally known as 3-D trilateral principle in mathematics. In case the computing of the positions through satellite signals is incorrect or affected due to atmospheric factor and resulting an error, the receiver is able to adjust the error with the assistance of a local broadcasting station in that particular area because the receiver is in constant communication with the local broadcasting station and because the local broadcasting station broadcasts radio signals with signal correction information for that particular area. Thus, the GPS receiver can figure out the exact location of the vehicle (hence the receiver) on earth regardless of the time, landscape and atmospheric conditions. It is in the trend to install the GPS receiver within the moving vehicle in order to facilitate the tracking of an intended route.
Nowadays, GPS technology is integrated in the electronic device (such as a PDA), and further network and information technologies are added, thus the electronic device as a whole is suitable for an individual requirement. The utility of GPS receiver crosses the boundary of vehicles and enters the consumer's daily life.
FIG. 1A is a schematic view of a prior art stationary GPS receiver while FIG. 1B is a block diagram representing the components for forming the prior art stationary GPS receiver of FIG. 1A. The prior art GPS receiver 1 accordingly includes an antenna unit 11, a signal processor 13, a micro controller 14, a micro processor 15 and a display panel 17. The antenna unit 11 is adapted to receive the satellite signal and later transmits the same to the signal processor 13 for processing (such as amplifying and filtering). The result is then transmitted to the micro processor 15. The GPS receiver stores some built-in software, such as navigation calculation programs, data processing programs and an almanac for computing the positions. The micro controller 14 orders the micro processor 15 to execute the analyzing and the computing operation. The final result (location of the vehicle) is shown in the display panel 17.
When the GPS receiver is installed in a vehicle, as shown in FIG. 1A, it is generally known as stationary since the position thereof cannot be changed according to the wishes of the driver. FIG. 1B is a block diagram representing the components for forming the prior art stationary GPS receiver of FIG. 1A. The prior art GPS receiver 1 accordingly includes an outer casing 10 disposed vertically (in C arrow direction) on a supporting surface, an antenna unit 11 (generally a patch antenna or inverted F-shaped antenna) is mounted on the casing 10 for receiving or transmitting signals. The antenna unit 11 is adapted to receive or transmit the signal at various angles. For the patch antenna, the signal-receiving direction tends upwardly from its mounting position. In order to achieve the great signal-receiving ability (i.e. a relatively strong satellite signal), the antenna unit 11 is mounted on a first lateral side 100 of the casing 10. Thus, its signal-receiving direction is in the arrow A direction, i.e. an upward direction.
FIG. 2 shows the prior art GPS receiver 1 in a portable mode (held within a user's hand). Under this condition, the direction of the display panel 17 is changed from that shown in FIG. 1A according to the user's holding habit. The display panel 17 in FIG. 2 has a narrower width but taller height, and extends in the vertical direction when compared with that of FIG. 1A. Because the position is changed, the second lateral side 101 of the casing 10 is located at the topside or the signal-receiving direction (arrow A direction) while the antenna unit 11 is disposed to extend. in the arrow D direction. When the prior art GPS receiver 1 is held as shown in FIG. 2, the signal-receiving strength thereof is reduced considerably because the orientation of the antenna unit 11 is transverse to the signal-receiving direction, thereby causing interruption in the signal transmission or delay in signal transmission.
It is the object of the present invention to propose a GPS receiver having an antenna unit capable of switching to a required direction so as to receive the incoming satellite signals and the switching method thereof.